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docs(api.md): add notes on race condition in page.setViewport #4319

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Jun 11, 2019
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docs(api.md): add notes on race condition in page.setViewport #4319

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docs(api.md): add notes on race condition in page.setViewport
aslushnikov Apr 20, 2019
ed3f7db
address comments
aslushnikov Jun 11, 2019
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@aslushnikov
aslushnikov committed Jun 11, 2019
commit ed3f7db2c1b37786a9401472df62ff613f7d2795
10 changes: 2 additions & 8 deletions docs/api.md
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Expand Up @@ -1237,11 +1237,7 @@ Emulates given device metrics and user agent. This method is a shortcut for call

To aid emulation, puppeteer provides a list of device descriptors which can be obtained via the [`puppeteer.devices`](#puppeteerdevices).

To avoid race condition with page's logic that sniffs for viewport and user
agent properties, it is recommended to call `page.emulate` *before* navigating
page to the target URL.

Example of emulating an iPhone 6 in puppeteer:
`page.emulate` will resize the page. A lot of websites don't expect phones to change size, so you should emulate before navigating to the page.
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This is even easier. The user agent needs to be sent before the first navigation.

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Fair! Keeping it as-is doesn't hurt.


```js
const puppeteer = require('puppeteer');
Expand Down Expand Up @@ -1804,9 +1800,7 @@ puppeteer.launch().then(async browser => {

In the case of multiple pages in a single browser, each page can have its own viewport size.

To avoid race condition with page's logic that sniffs for viewport properties,
it is recommended to call `page.setViewport` *before* navigating page to the target
URL.
`page.setViewport` will resize the page. A lot of websites don't expect phones to change size, so you should set the viewport before navigating to the page.

```js
const page = await browser.newPage();
Expand Down